Bionic Knee Research

Dr. Rouse was a Postdoctoral Fellow in the Biomechatronics Group at the MIT Media Lab from 2012 – 2014. This is a summary of some of his work during his time at MIT.

Currently, the mobility of above knee amputees is limited by the lack of available prostheses that can efficiently replicate biologically accurate movements. In this project, a powered knee prosthesis was designed utilizing a novel mechanism, known as a clutchable series-elastic actuator (CSEA). The CSEA includes a low-power clutch in parallel with an electric motor within a traditional series-elastic actuator. The stiffness of the series elasticity was tuned to match the elastically conservative region of the knee’s torque-angle relationship during the stance phase of locomotion. During this region, the clutch was used to efficiently store energy in the series elasticity. The fully autonomous knee prosthesis design utilized a brushless electric motor, ballscrew transmission and cable drive. Furthermore, the CSEA knee uses a 400W commercially-available brushless motor controller with a Raspberry Pi computer as host. As such, it is the first lower-extremity robotic prosthesis to run a full operating system installation, Linux Debian, complete with wireless internet and USB ports. It has integrated 16-bit data acquisition and load sensing. The CSEA knee was lighter than the 8th percentile and shorter than the 1st percentile male shank segment. When tested with a unilateral above knee amputee walking at 1.3 m/s, the CSEA Knee provided biomechanically accurate torque-angle behavior, agreeing within 17% of the net work and 27% of the stance flexion angle produced by the biological knee. Additionally, the process of locomotion reduced the net electrical energy consumption of the CSEA Knee. The knee’s motor generated 1.8 J/stride, and the net energy consumption was 3.6 J/stride, an order of magnitude less energy than previously published state-of-the-art powered knee prostheses. Future work will focus on a custom, power-optimized embedded system and the expansion of the CSEA architecture to other biomechanically relevant joints for bionic prosthesis development.

A Reddit response related to this work was responsible for 20k hits to this webpage in two days. In order to make the science and engineering of this (and other) projects more accessible, a friend/colleague and I did a Reddit Ask Me Anything (AMA). We fielded many questions related to my work here and the state-of-the-art in bionic systems; it was really rewarding to chat with people and provide some insight into the world of biomechatronics and academic engineering.

The MIT CSEA Knee is being tested with the BiOM powered ankle foot prosthesis. In this configuration, the bionic leg was able to operate at nearly energy neutral–where it generated almost as much energy as it consumed during walking.

Testing of the hardware and software behind the MIT CSEA Robotic Knee. The finite state machine is tuned over the wireless network and gait parameters are assessed. The finite state machine alternates between four states that provide walking behavior, with the LED indicating the current controller state.

Video of CSEA Knee exploded view showcasing parts within the total device. The explosion also animates the process by which the device is assembled. For a higher resolution version of the video, see the Vimeo site.